Oil pumps as conventionally used in internal combustion engines are of the gear pump type in which the teeth of a drive gear mesh with teeth of a driven gear within a cavity provided in the oil pump housing. One side of the drive gear is axially rotated by a drive shaft which extends through the housing whilst the corresponding side of the driven gear is axially supported for rotation from said housing on an idler shaft. During rotation of the gears within the housing cavity, oil is drawn into the cavity in an area where the teeth of the meshing gears diverge while oil under pressure is discharged from the cavity in an area where the teeth of the meshing gears converge.
As disclosed by Gary A. Cross et al. in U.S. Pat. No. 5,810,571 which issued on Sep. 22, 1998, a preferred form of high performance oil pump construction, in order to minimize wear in the oil pump while generating high oil flow necessary to lubricate an engine rotating at high RPM requires, inter alia, drive and driven pump gears that are rotatably supported on shafts within bearings located on the opposite side of the two gears. As disclosed in this patent, the gear shafts of the drive and driven gears which rotate with the drive and driven gears have the shafts on the upper side of the gears supported in the upper housing of the pump while the gear shafts on the opposite side of the gears are rotatably supported in bearing bores provided in the lower pump housing.
Since the weight of a performance or competition internal combustion engine is of importance, the oil pumps used in them normally employ an aluminum housing with the drive and driven gears and their associated shafts being fabricated from steel. An inherent shortcoming which exists in high performance aluminum oil pumps as disclosed in the '571 patent, is that the ends of the bearing shafts of the steel drive and driven gears which are rotatably received in the bearing bores provided in the lower aluminum housing, even though they are subjected to direct lubrication, can become enlarged and oval in shape due to a cantilevering effect experienced at the bottom end of the drive and driven gears which undergo significant stress when producing, within the housing, large quantities of lubricating oil under high pressure.